1. Field of the Invention
The present invention relates to a magneto-resistive element widely used for, for example, a magnetic head for reproducing information recorded on a magnetic medium such as a magnetic disc, an optical magnetic disc, a magnetic tape or the like, for a magnetic sensor used in an automobile or the like, and a magnetic random access memory (MRAM).
2. Description of the Related Art
In accompaniment with recent improvement in the magnetic recording density, a spin valve type GMR (giant magneto-resistive) element has been put into practice. A spin valve type GMR is described as operating on a fundamental principle that a mean free path of electrons flowing in a layer along a direction parallel to a layer surface changes in accordance with a relative magnetization angle between a free layer and a fixed layer. A spin valve type GMR provides an MR ratio (magneto-resistive ratio) of about 10%, which is several times higher than that of a conventional anisotropic MR element.
As elements providing a still higher MR ratio than that of the spin valve type GMR, a TMR element using a TMR (tunneling magneto-resistive) effect and a CPP (current perpendicular to the plane) GMR element using a magnetic metal/transfer metal artificial lattice are now being studied.
A CPP GMR element basically operates on the same principle as that of the above-mentioned spin valve type GMR element. In the CPP GMR element, however, a current flows along a direction perpendicular to the layer surface. A TMR element is a new magneto-resistive element using a tunneling probability of electrons which changes in accordance with the relative magnetization angle between two ferromagnetic layer interposing a tunneling insulating layer, in the TMR element, a current flows in a direction perpendicular to the layer surface, like the above-mentioned CPP GMR element. In this specification, a TMR element and a CPP GMR element in which a current flows in a direction perpendicular to the layer surface will be collectively referred to as a xe2x80x9cvertical current type magneto-resistive elementxe2x80x9d.
Various structures for using a vertical current type magneto-resistive element for a magnetic head have been proposed. Japanese Laid-Open Publication No. 11-213349 proposes a shield type magnetic head including a TMR element, instead of a spin valve type GMR element, and including a flux guide. Japanese Laid-Open Publication No. 11-25425 proposes a magnetic head including a TMR element inside a yoke formed in a direction perpendicular to a surface of a magnetic recording medium.
When a TMR element is used for a magnetic head, there are problems that, due to an essentially high junction impedance of the TMR element, thermal noise is generated and the TMR element does not match an electric circuit for driving the TMR element.
An increase in the area of the TMR element in order to reduce the junction impedance causes another problem that it becomes difficult to reduce the size of the magnetic head. Such an increase in the area of the TMR element also causes a problem that it becomes difficult to improve the sensitivity of the magnetic head because a magnetic flux leaking from a surface of a magnetic recording medium increases as the recording density is improved.
A reduction in the thickness of the tunneling insulating layer of the TMR element in order to reduce the junction impedance also causes the following problem. Such a reduction strengthens the magnetic bonding between the ferromagnetic layers interposing the tunneling insulating layer. Therefore, it becomes difficult to realize an ideal relative magnetization angle, which makes it difficult to provide a high MR ratio.
A reduction in the distance between the TMR element and the magnetic recording medium in order to improve the sensitivity of the magnetic head causes a problem that a contact of the TMR element with the magnetic recording medium generates a thermal spike.
The above-mentioned conventional structures for using a vertical current type magneto-resistive element have problems of pulse amplitude asymmetry and asymmetry of side reading may undesirably occur.
A common problem among magnetic heads and MRAMs, the size of which is now being reduced, is that when the amount of a current flowing in the TMR element increases, a magnetic field generated based on the current causes an unfavorable influence on the magnetization direction of the free layer (or the magnetic field sensing section).
A TMR element has an inherent problem of bias voltage dependence such that when the bias voltage applied on the TMR element is increased, the MR ratio is decreased.
In order to apply a bias magnetic field on a vertical current type magneto-resistive element, it is necessary to provide an anti-ferromagnetic member for generating a bias magnetic field or it is necessary to provide a magnetic body forming the vertical current type magneto-resistive element with anisotropy by heat-treating the magnetic body in a magnetic field.
According to one aspect of the invention, a magneto-resistive element includes a vertical current type magneto-resistive element; a first conductor for causing a current to flow into the vertical current type magneto-resistive element; and a second conductor for causing the current to flow out of the vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current. The second conductor generates a second magnetic field based on the current. The first conductor and the second conductor are located so that the first magnetic field and the second magnetic field act as a bias magnetic field applied on the vertical current type magneto-resistive element.
In one embodiment of the invention, the first conductor and the second conductor are located parallel to each other.
In one embodiment of the invention, the magneto-resistive element is substantially U-shaped.
In one embodiment of the inventions the first conductor and the second conductor are located twisted to each other.
According to another aspect of the invention, a magneto-resistive element includes a vertical current type magneto-resistive element; a first conductor for causing a current to flow into the vertical current type magneto-resistive element; and a second conductor for causing the current to flow out of the vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current,
the second conductor generates a second magnetic field based on the current. The first conductor and the second conductor are located so that the second magnetic field cancels at least a part of the first magnetic field.
In one embodiment of the invention, the first conductor and the second conductor are located parallel to each other.
According to still another aspect of the invention, a multiple element magneto-resistive device includes a first vertical current type magneto-resistive element responding to a specific external magnetic field; a second vertical current type magneto-resistive element responding to the specific external magnetic field; and a yoke on which the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are provided.
In one embodiment of the invention, the multiple element magneto-resistive device further includes an adder for adding an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element so as to detect the specific external magnetic field.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a subtracter for processing an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element with subtraction so as to detect the specific external magnetic field.
In one embodiment of the invention, each of the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element includes a fixed layer, a magnetization direction of which does not change even when a magnitude of the specific external magnetic field is changed, and a non-magnetic layer provided between the fixed layer and the yoke. The yoke acts as a free layer, a magnetization direction of which changes in accordance with a change in the magnitude of the specific external magnetic field.
According to still another aspect of the invention, a multiple element magneto-resistive device includes a first vertical current type magneto-resistive element responding to a specific external magnetic field; and a second vertical current type magneto-resistive element responding to the specific external magnetic field. The first vertical current type magneto-resistive element generates a first magnetic field based on a current therein. The second vertical current type magneto-resistive element generates a second magnetic field based on a current therein. The first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are located so that the first magnetic field and the second magnetic field act as a bias magnetic field applied on the multiple element magneto-resistive device.
In one embodiment of the invention, the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are electrically connected to each other in series.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a first conductor for causing the current to flow into the first vertical current type magneto-resistive element, a second conductor for causing the current flowing out of the first vertical current type magneto-resistive element to flow into the second vertical current type magneto-resistive element, and a third conductor for causing the current to flow out of the second vertical current type magneto-resistive element.
In one embodiment of the invention, the first vertical current type magneto-resistive element is located on the same side as the second vertical current type magneto-resistive element with respect to the second conductor.
In one embodiment of the invention, the first vertical current type magneto-resistive element is located on an opposite side to the second vertical current type magneto-resistive element with respect to the second conductor.
In one embodiment of the invention, the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are electrically connected to each other in parallel.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a first conductor for causing the current to flow into the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element, and a second conductor for causing the current to flow out of the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a first conductor for causing the current to flow into the first vertical current type magneto-resistive element, a second conductor for causing the current to flow out of the first vertical current type magneto-resistive element, a third conductor for causing the current to flow into the second vertical current type magneto-resistive element, and a fourth conductor for causing the current to flow out of the second vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current flowing therein. The second conductor generates a second magnetic field based on the current flowing therein. The first conductor and the second conductor are located so that the first magnetic field and the second magnetic field act as a bias magnetic field applied on the first vertical current type magneto-resistive element. The third conductor generates a third magnetic field based on the current flowing therein. The fourth conductor generates a fourth magnetic field based on the current flowing therein. The third conductor and the fourth conductor are located so that the third magnetic field and the fourth magnetic field act as a bias magnetic field applied on the second vertical current type magneto-resistive element.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a first conductor for causing the current to flow into the first vertical current type magneto-resistive element, a second conductor for causing the current to flow out of the first vertical current type magneto-resistive element, a third conductor for causing the current to flow into the second vertical current type magneto-resistive element, and a fourth conductor for causing the current to flow out of the second vertical current type magneto-resistive element. The first conductor generates a first magnetic field based on the current flowing therein. The second conductor generates a second magnetic field based on the current flowing therein. The first conductor and the second conductor are located so that the first magnetic field and the second magnetic field cancel each other. The third conductor generates a third magnetic field based on the current flowing therein. The fourth conductor generates a fourth magnetic field based on the current flowing therein. The third conductor and the fourth conductor are located so that the third magnetic field and the fourth magnetic field cancel each other.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a yoke on which the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are provided.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a substrate provided on an opposite side to the first and second vertical current type magneto-resistive elements with respect to the yoke.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a substrate provided on an opposite side to the yoke with respect to the first and second vertical current type magneto-resistive elements.
In one embodiment of the invention, the yoke is a horizontal yoke.
In one embodiment of the invention, the yoke is a vertical yoke.
In one embodiment of the invention, each of the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element includes an anti-ferromagnetic layer: a fixed layer; and a non-magnetic layer provided on an opposite side to the anti-ferromagnetic layer with respect to the fixed layer.
In one embodiment of the invention, the multiple element magneto-resistive device further includes an adder for adding an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element so as to detect the specific external magnetic field.
In one embodiment of the invention, the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element have different polarities from each other.
In one embodiment of the invention, the multiple element magneto-resistive device further includes a subtractor for processing an output of the first vertical current type magneto-resistive element and an output of the second vertical current type magneto-resistive element with subtraction so as to detect the specific external magnetic field.
In one embodiment of the invention, the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element have different polarities from each other.
In one embodiment of the invention, the first and second vertical current type magneto-resistive elements detect a change in a relative magnetization angle between at least two magnetic bodies as a change in a tunneling probability of electrons.
In one embodiment of the invention, the first and second vertical current type magneto-resistive elements detect a change in a relative magnetization angle between at least two magnetic bodies as a change in a mean free path of electrons.
According to still another aspect of the invention, a magnetic random access memory includes a multiple element magneto-resistive device. The multiple element magneto-resistive device includes a first vertical current type magneto-resistive element responding to a specific external magnetic field; and a second vertical current type magneto-resistive element responding to the specific external magnetic field. The first vertical current type magneto-resistive element generates a first magnetic field based on a current therein. The second vertical current type magneto-resistive element generates a second magnetic field based on a current therein. The first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are located so that the first magnetic field and the second magnetic field act as a bias magnetic field applied on the multiple element magneto-resistive device.
In one embodiment of the invention, the first vertical current type magneto-resistive element and the second vertical current type magneto-resistive element are electrically connected to each other in series.
In one embodiment of the invention, the magnetic random access memory further includes a first conductor for causing the current to flow into the first vertical current type magneto-resistive element, a second conductor for causing the current flowing out of the first vertical current type magneto-resistive element to flow into the second vertical current type magneto-resistive element, and a third conductor for causing the current to flow out of the second vertical current type magneto-resistive element.
In one embodiment of the invention, the first vertical current type magneto-resistive element is provided on an opposite side to the second vertical current type magneto-resistive element with respect to the second conductor.
Thus, the invention described herein makes possible the advantages of providing (1) a magneto-resistive element and a multiple element magneto-resistive device for adjusting a bias magnetic field applied on a vertical current type magneto-resistive element therein with a simple structure; (2) a magneto-resistive element and a multiple element magneto-resistive device having a high sensitivity; (3) a magneto-resistive element and a multiple element magneto-resistive device for reducing a thermal spike generated by the contact of a magnetic head and a magnetic recording medium; (4) a compact magneto-resistive element and a compact multiple element magneto-resistive device for providing a high output; and (5) a magneto-resistive element and a multiple element magneto-resistive device for preventing pulse amplitude asymmetry and asymmetric side reading.
These and other advantages of the present invention will become apparent to those skilled in the art upon reading and understanding the following detailed description with reference to the accompanying figures.